Formulae and expressions A3.1 Core Plenary Solve these problems – use the method you think is easiest. I think of a number, subtract 3 and multiply by 4. The final answer is 12. What number did I think of? I think of a number, divide by 3 and add 4. The final answer is 19. I think of a number, multiply by 3 and subtract 3. Can you explain your method? Are there other ways to solve these problems? Make up some similar ‘I think of a number …’ problems for yourselves. Preamble These problems may be solved using trial and improvement, by inspection or using inverse functions. Initially allow pupils to use the method they feel most comfortable with, but by the end they should appreciate the advantages of using inverse functions. The usefulness of any subsequent discussion as a result of making up their own problems cannot be stressed too much. Possible content Solving simple problems using trial and improvement or inverse functions. Resources None. Solution/Notes 6, 45, 5.